Italian Patent Applications No. MI2005A001752 and No. MI2007A001685 show a reactor of this type, wherein a substantially cylindrical separation structure delimits a central hot header and an annular cold header, which surrounds the hot header; the cold header houses a plurality of integrated heat-exchange units, each of which includes a pump and one or two heat exchangers; each integrated unit has an inlet connected to the hot header through specially provided ducts for the primary fluid.
However, these solutions, like others generically similar with heat exchangers of different configuration, are not devoid of drawbacks, especially in terms of dimensions, in particular due to the complexity of the canalization system of the primary fluid and inadequate utilization of the spaces. The pump-exchanger units must be housed outside the separation structure between the hot header and cold header, but said structure has a relatively large diameter because it contains the core and usually the neutron shielding elements of the structure. The pump-exchanger units are thus installed in a circumferential position with respect to the centre of the reactor, with a consequent increase in the diameter of the reactor vessel, which contains all the components of the primary system.
Documents US2013/266111, EP0308691 and JPH06174871 usefully have a separation structure of smaller diameter in the upper part and larger diameter in the lower part. In these solutions, the refrigerant fluid exiting from the core rises inside the separation structure to its upper edge, where the direction reverses to top-down feed the heat exchanger units. Similarly, these solutions are not without drawbacks, such as the constructional complexity of the zone of fluid direction reversal and the risk of entraining blanket gas that, in the case where the refrigerant fluid is a liquid metal, could cause accidental positive reactivity insertions in the core.